This environmentally friendly quantum sensor runs on sunlight

Quantum technology goes green.

A new version of highly sensitive magnetic field sensors does away with the power-hungry lasers that previous devices relied on to make their measurements, and replaces them with sunlight. Lasers can consume about 100 watts of power – like keeping a bright lightbulb burning. The innovation may relieve quantum sensors of this energy requirement. The result is a state-of-the-art, eco-friendly prototype, researchers report in an upcoming issue of Physical Check X Energy.

The big twist is in how The device uses sunlight. It does not use solar cells to convert light into electricity. Instead, sunlight does the job of laser light, says Jiangfeng Du, a physicist at the University of Science and Technology of China in Hefei.

Quantum magnetometers often include a powerful green laser to measure magnetic fields. The laser shines on a diamond that contains atomic defects (SN: 02/26/08). The defects are created when nitrogen atoms replace some of the carbon atoms that make up pure diamonds. The green laser causes the nitrogen defects to fluoresce, emitting red light whose intensity depends on the strength of the surrounding magnetic fields.

The new quantum sensor also needs the green light. This is plentiful in sunlight, as seen in the green wavelengths reflected off tree leaves and grass. To collect enough of it to power their magnetometer, Du and his colleagues replaced the laser with a 15 centimeter diameter lens to collect sunlight. Then they filtered the light to remove all colors except green and focused it on a diamond with nitrogen atom defects. The result is a red fluorescence that indicates magnetic field strengths, just like laser-equipped magnetometers.

A prototype lens filters green light from sunlight onto a diamond-based sensor below.
Green light shining on the diamond-based sensor in a quantum device can be used to measure magnetic fields. In this prototype, a lens (above) collects sunlight that is filtered to leave only green wavelengths of light. This green light offers an environmentally friendly alternative to the light produced by energy-hungry lasers that traditional quantum devices rely on.Yunbin Zhu/University of Science and Technology of China

Switching energy from one type to another, as happens when solar cells collect light and generate electricity, is an inherently inefficient process (SN: 07/26/17). The researchers claim that avoiding the conversion of sunlight into electricity to power lasers makes their approach three times more efficient than would be possible with solar cells powering lasers.

“I’ve never seen other reports linking solar research to quantum technologies,” says Yen-Hung Lin, a physicist at the University of Oxford who wasn’t involved in the study. “It could well spark an interest in this unexplored direction, and we could see more interdisciplinary research in the field of energy.”

Quantum devices sensitive to other things, like electric fields or pressure, could also benefit from the sunlight-driven approach, the researchers say. In particular, space-based quantum technology could harness the intense sunlight outside of Earth’s atmosphere to provide light tailored to quantum sensors. The remaining light in wavelengths that the quantum sensors don’t use could be relegated to solar cells that power the electronics that process the quantum signals.

The sunlight-powered magnetometer is just a first step in the merging of quantum and green technology. “In its current state, this device is primarily for development purposes,” says Du. “We expect that the devices will be used for practical purposes. But there [is] a lot to do.”

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